| Description:The Quaternion_Base class defines a quaternion that represents rotation between two right-handed reference frames. In this dictionary, quaternions are always constructed so that the application of the quaternion describes the rotation of one frame to a second frame. The two frames and the direction of rotation must be identified unambiguously in the enclosing classes. Quaternions are expressed as a set of four numbers in the order (qcos, qsin1, qsin2, qsin3), where qcos = cos(theta/2) and qsin(n) = sin(theta/2)*a(n). Theta is the angle of rotation and a is the unit vector (x,y,z) around which the rotation occurs. A document providing the full mathematical basis for this construction, along with examples, and a summary of common pitfalls, is in preparation. The current version can be obtained by contacting the PDS Engineering Node. In application you need to know the four elements of the quaternion, the two end point frames, and the direction of the rotation. This dictionary provides two extensions to this Base class. In the Quaternion_Plus_Direction class we require the direction of rotation. This class can only be used if the two end point frames are identified in the enclosing class. This is generally the case in the Lander section. The Quaternion_Plus_To_From class requires the two frames be identified explicitly with one designated as the "from frame" and the other as the "to frame". |